Various types of boom assemblies for use in cranes or other lifting devices are known in the art. Generally, conventional mobile cranes have an extendable boom assembly including base section carrying a plurality of telescoping boom sections. As should be appreciated, the base section must be designed to carry the full weight of the boom when fully extended, plus any corresponding load being lifted.
While the solution to increasing boom strength would seem to dictate simply adding to the thickness of the shell forming the base section, this competes with the goal of lowering the weight of the boom as much as possible, not only for purposes of lifting power constraints, but also for over-the-road travel (for which there are typically stringent weight restrictions to avoid damage to the roadway). Adding thickness to the material forming the shell also greatly complicates the manufacturing process, since the boom is typically a rounded structure requiring difficult and costly metalworking processes, such as breaking and welding. Moreover, welding a “doubler” directly to the rounded underside of the primary shell to increase the overall thickness of the boom typically causes undesirable deformation in the underlying material.
Accordingly, there is a need for a mobile crane having a telescoping boom that is capable of achieving a more desirable balance between added strength and reduced weight, without unduly complicating the manufacturing process or increasing the resulting cost.